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{{Short description|Coordination of events to operate a system in unison}}
{{Other uses}}
{{Use dmy dates|date=September
[[File:Rockettes 2239918515 96df95270e.jpg|thumb|Synchronized dancers]]
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In [[electrical engineering]] terms, for digital logic and data transfer, a [[synchronous circuit]] requires a [[clock signal]]. A clock signal simply signals the start or end of some time period, often measured in microseconds or nanoseconds, that has an arbitrary relationship to any other system of measurement of the passage of minutes, hours, and days.
In a different sense, electronic systems are sometimes synchronized to make events at points far apart appear simultaneous or near-simultaneous from a certain perspective.{{efn|Albert Einstein proved in 1905 in his first relativity paper that there actually are no such things as absolutely simultaneous events.}} Timekeeping technologies such as the [[
In [[computer science]] (especially [[parallel computing]]), synchronization is the coordination of simultaneous [[thread (computing)|threads]] or [[Process (computing)|processes]] to complete a task with correct runtime order and no unexpected [[race condition]]s; see [[synchronization (computer science)]] for details.
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{{See also|Synchronization of chaos}}
Synchronization of multiple interacting [[dynamical system]]s can occur when the systems are [[Self-oscillation|autonomous oscillators]]. Poincaré phase oscillators are model systems that can interact and partially synchronize within random or regular networks.<ref name="Nolte">{{cite book | first = David | last = Nolte | title = Introduction to Modern Dynamics: Chaos, Networks, Space and Time | publisher = [[Oxford University Press]] | year = 2015 }}</ref> In the case of global synchronization of phase oscillators, an abrupt transition from unsynchronized to full synchronization takes place when the coupling strength exceeds a critical threshold. This is known as the [[Kuramoto model]] [[phase transition]].<ref name=":1">{{Cite web|url=https://www.youtube.com/watch?v=t-_VPRCtiUg|title = The Surprising Secret of Synchronization|website = [[YouTube]]| date=31 March 2021 }}</ref> Synchronization is an emergent property that occurs in a broad range of dynamical systems, including neural signaling, the beating of the heart and the synchronization of fire-fly light waves. A unified approach that quantifies synchronization in chaotic systems can be derived from the statistical analysis of measured data.<ref>{{Cite journal|last1=Shah|first1=Dipal| last2=Springer|first2=Sebastian|last3=Haario|first3=Heikki|last4=Barbiellini|first4=Bernardo|last5=Kalachev|first5=Leonid|date=2023|title= Data based quantification of synchronization|journal=Foundations of Data Science|volume=5|issue=1|pages=152–176|doi=10.3934/fods.2022020|doi-access=free}}</ref>
=== Neuroscience ===
In cognitive neuroscience, (stimulus-dependent) (phase-)synchronous oscillations of neuron populations serve to solve the general
▲== Applications ==
===
In cognitive science, integrative (phase) synchronization mechanisms in cognitive neuroarchitectures of modern [[connectionism]] that include coupled oscillators (e.g."Oscillatory Networks"<ref>Werning, M. (2012). Non-symbolic compositional representation and its neuronal foundation: Towards an emulative semantics. In M. Werning, W. Hinzen & E. Machery (eds.), The Oxford handbook of compositionality (pp. 633-654). Oxford University Press. Oxford.</ref>) are used to solve the [[binding problem]] of cognitive neuroscience in perceptual cognition ("feature binding") and in language cognition ("variable binding").<ref>Maurer, H. (2021). ''Cognitive science: Integrative synchronization mechanisms in cognitive neuroarchitectures of the modern connectionism''. CRC Press, Boca Raton/FL, {{ISBN
▲In cognitive neuroscience, (stimulus-dependent) (phase-)synchronous oscillations of neuron populations serve to solve the general "[[binding problem]]". According to the so-called "Binding-By-Synchrony (BBS) Hypothesis"<ref>Singer, W. (1999). Neuronal synchrony: A versatile code for the definition of relations. Neuron, 24, 49-65.</ref><ref>Singer, W. (1999a). Binding by neural synchrony. In R. A. Wilson & F. C. Keil (eds.): The MIT encyclopedia of the cognitive sciences (pp. 81-84). Cambridge, MA, London: The MIT Press.</ref><ref>Singer, W. (2009a). Consciousness and neuronal synchronization. In S. Laureys & G. Tononi: The neurology of consciousness: Cognitive neuroscience and neuropathology (pp. 43-52). Amsterdam: Elsevier.</ref><ref>Singer, W. (2009b). Neural synchrony and feature binding. In L.R. Squire (Ed.) Encyclopedia of Neuroscience. Vol. 6 (pp. 253-259). Oxford: Academic Press.</ref><ref>Singer, W. (2013a). The neuronal correlate of consciousness: Unity in time rather than space? Neurosciences and the Human Person: New Perspectives on Human Activities Pontifical Academy of Sciences. Scripta Varia. Vol. 121. Vatican City. 2013. From: www.casinapioiv.va/content/dam/accademia/pdf/sv121/sv121-singer.pdf</ref><ref>Singer, W. (2013b). Cortical dynamics revisited. Trends in Cognitive Sciences 17, 616-626.</ref><ref>Singer, W. (2018). Neuronal oscillations: unavoidable and useful? European Journal of Neuroscience 48, 2389-2399.</ref> a precise temporal correlation between the impulses of neurons ("cross-correlation analysis"<ref>Engel, A. K., König, P., Gray, C. M. & Singer, W. (1990). Stimulus-dependent neuronal oscillations in cat visual cortex: Intercolumnar interaction as determined by cross-correlation analysis. European Journal of Neuroscience, 2, 588-606.</ref>) and thus a stimulus-dependent temporal synchronization of the coherent activity of subpopulations of neurons emerges. Moreover, this synchronization mechanism circumvents the "superposition problem"<ref>Malsburg, C. von der (1999). The what and why of binding: The modeler's perspective. Neuron, 24, 95-104.</ref> by more effectively identifying the signature of synchronous neuronal signals as belonging together for subsequent (sub-)cortical information processing areas.
===
There is a concept that the synchronization of biochemical reactions determines biological [[homeostasis]]. According to this theory, all reactions occurring in a living cell are synchronized in terms of quantities and timescales to maintain [[biological network]] functional.<ref>{{cite journal |last1=Hołyst |first1=Robert |last2=Bubak |first2=Grzegorz |last3=Kalwarczyk |first3=Tomasz |last4=Kwapiszewska |first4=Karina |last5=Michalski |first5=Jarosław |last6=Pilz |first6=Marta |title=Living Cell as a Self-Synchronized Chemical Reactor |journal=J. Phys. Chem. Lett. |date=2024 |volume=15 |issue=13 |pages=3559–3570 |doi=10.1021/acs.jpclett.4c00190|doi-access=free |pmid=38526849 |pmc=11000238 }}</ref>
▲In cognitive science, integrative (phase) synchronization mechanisms in cognitive neuroarchitectures of modern [[connectionism]] that include coupled oscillators (e.g."Oscillatory Networks"<ref>Werning, M. (2012). Non-symbolic compositional representation and its neuronal foundation: Towards an emulative semantics. In M. Werning, W. Hinzen & E. Machery (eds.), The Oxford handbook of compositionality (pp. 633-654). Oxford University Press. Oxford.</ref>) are used to solve the [[binding problem]] of cognitive neuroscience in perceptual cognition ("feature binding") and in language cognition ("variable binding").<ref>Maurer, H. (2021). Cognitive science: Integrative synchronization mechanisms in cognitive neuroarchitectures of the modern connectionism. CRC Press, Boca Raton/FL, ISBN 978-1-351-04352-6. https://doi.org/10.1201/9781351043526</ref><ref>Maurer, H. (2016). „Integrative synchronization mechanisms in connectionist cognitive Neuroarchitectures“. Computational Cognitive Science. 2: 3. https://doi.org/10.1186/s40469-016-0010-8</ref><ref>Marcus, G.F. (2001). The algebraic mind. Integrating connectionism and cognitive science. Bradford Book, The MIT Press, Cambridge, ISBN 0-262-13379-2. https://doi.org/10.7551/mitpress/1187.001.0001</ref><ref>Bechtel,W. & Abrahamsen, A.A. (2002). Connectionism and the Mind: Parallel Processing, Dynamics, and Evolution in Networks. 2nd Edition. Blackwell Publishers, Oxford.</ref>
== Human movement ==
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Synchronization of movement is defined as similar movements between two or more people who are temporally aligned.<ref>{{Cite journal|last1=Condon|first1=W. S.|last2=Ogston|first2=W. D.|date=1 October 1966|title=Sound film analysis of normal and pathological behavior patterns|journal=The Journal of Nervous and Mental Disease|volume=143|issue=4|pages=338–347|issn=0022-3018|pmid=5958766|doi=10.1097/00005053-196610000-00005|s2cid=19384588}}</ref> This is different from mimicry, which occurs after a short delay.<ref>{{Cite journal|last1=Richardson|first1=Michael J.|last2=Marsh|first2=Kerry L.|last3=Schmidt|first3=R. C.|date=1 February 2005|title=Effects of visual and verbal interaction on unintentional interpersonal coordination|journal=Journal of Experimental Psychology. Human Perception and Performance|volume=31|issue=1|pages=62–79|doi=10.1037/0096-1523.31.1.62|issn=0096-1523|pmid=15709863|citeseerx=10.1.1.176.8093}}</ref> [[Line dance]] and [[military step]] are examples.
[[Muscular bonding]] is the idea that moving in time evokes particular emotions.<ref>{{Cite book|url=https://books.google.com/books?id=F5QqSt6umWsC|hdl=2027/heb.04002.0001.001|title=Keeping Together in Time|isbn=978-0-674-50230-7|last1=McNeill|first1=William Hardy|date=30 September 1997|publisher=Harvard University Press }}</ref> This sparked some of the first research into movement synchronization and its effects on human emotion. In groups, synchronization of movement has been shown to increase conformity,<ref>{{Cite journal|last1=Dong|first1=Ping|last2=Dai|first2=Xianchi|last3=Wyer|first3=Robert S.|date=1 January 2015|title=Actors conform, observers react: the effects of behavioral synchrony on conformity|journal=Journal of Personality and Social Psychology|volume=108|issue=1|pages=60–75|doi=10.1037/pspi0000001|issn=1939-1315|pmid=25437130}}</ref> cooperation and trust.<ref>{{Cite web|url=https://pubmed.ncbi.nlm.nih.gov/?term=Synchrony+and+Cooperation|title=Synchrony and Cooperation – PubMed – Search Results|access-date=2017-02-02}}</ref>{{Failed verification|date=October 2019}}
In [[Dyad (sociology)|dyads]], groups of two people, synchronization has been demonstrated to increase affiliation,<ref name=":0">{{Cite journal|doi=10.1521/soco.2009.27.6.949 |title=It's All in the Timing: Interpersonal Synchrony Increases Affiliation |journal=Social Cognition |volume=27 |issue=6 |pages=949 |year=2009 |last1=Hove |first1=Michael J. |last2=Risen |first2=Jane L. }}</ref> self-esteem,<ref>{{Cite journal|last1=Lumsden|first1=Joanne|last2=Miles|first2=Lynden K.|last3=Macrae|first3=C. Neil|date=1 January 2014|title=Sync or sink? Interpersonal synchrony impacts self-esteem|journal=Frontiers in Psychology|volume=5|pages=1064|doi=10.3389/fpsyg.2014.01064|pmc=4168669|pmid=25285090|doi-access=free}}</ref> compassion and altruistic behaviour<ref>{{Cite journal|last1=Valdesolo|first1=Piercarlo|last2=Desteno|first2=David|date=1 April 2011|title=Synchrony and the social tuning of compassion|journal=Emotion|volume=11|issue=2|pages=262–266|doi=10.1037/a0021302|issn=1931-1516|pmid=21500895}}</ref> and increase rapport.<ref>{{Cite journal|last1=Vacharkulksemsuk|first1=Tanya|last2=Fredrickson|first2=Barbara L.|date=1 January 2012|title=Strangers in sync: Achieving embodied rapport through shared movements|journal=Journal of Experimental Social Psychology|volume=48|issue=1|pages=399–402|doi=10.1016/j.jesp.2011.07.015|issn=0022-1031|pmc=3290409|pmid=22389521}}</ref> During arguments, synchrony between the arguing pair has been noted to decrease
There has been dispute regarding the true effect of synchrony in these studies. Research in this area detailing the positive effects of synchrony, have attributed this to synchrony alone; however, many of the experiments incorporate a shared intention to achieve synchrony. Indeed, the Reinforcement of Cooperation Model suggests that perception of synchrony leads to reinforcement that cooperation is occurring, which leads to the pro-social effects of synchrony.<ref>{{Cite journal|last1=Reddish|first1=Paul|last2=Fischer|first2=Ronald|last3=Bulbulia|first3=Joseph|date=1 January 2013|title=Let's dance together: synchrony, shared intentionality and cooperation|journal=PLOS ONE|volume=8|issue=8|pages=e71182|doi=10.1371/journal.pone.0071182|issn=1932-6203|pmc=3737148|pmid=23951106|bibcode=2013PLoSO...871182R|doi-access=free}}</ref> More research is required to separate the effect of intentionality from the beneficial effect of synchrony.<ref>{{Cite journal|last1=Ellamil|first1=Melissa|last2=Berson|first2=Josh|last3=Margulies|first3=Daniel S.|date=1 January 2016|title=Influences on and Measures of Unintentional Group Synchrony|journal=Frontiers in Psychology|volume=7|pages=1744|doi=10.3389/fpsyg.2016.01744|pmc=5101201|pmid=27881968|doi-access=free}}</ref>
== Uses ==
Synchronization is important in [[digital telephony]], video and [[digital audio]] where streams of sampled data are manipulated. Synchronization of image and sound was an important technical problem in [[sound film]]. More sophisticated film, video, and [[sound|audio]] applications use [[time code]] to synchronize audio and video.
In [[electric power]] systems, [[alternator synchronization]] is required when multiple generators are connected to an electrical grid.
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[[Flash synchronization]] synchronizes the [[Flash (photography)|flash]] with the [[Shutter (photography)|shutter]].
Some systems may be only approximately synchronized, or [[plesiochronous]]. Some applications require that relative offsets between events be determined. For others, only the [[Partially ordered set|order]] of the event is important.
== See also ==
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* [[Phase synchronization]]
* [[Reciprocal socialization]]
* [[Synchronization (alternating current)]]
* [[Synchronization of chaos]]
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* [[Synchronous conferencing]]
* [[Timing synchronization function]] (TSF)
* [[Neural synchrony]]
;Order synchronization and related topics
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